1. Field of the Invention
This invention relates to a dashpot for controlling and slowing down the closing motion of the throttle valve in the carburetors of internal-combustion engines for automobiles and the like. More particularly, the invention is concerned with a fitting including a calibrated bleed orifice formed therein, not in one piece with, but as a separate component of, the dashpot body.
2. Brief Description of the Prior Art
The prior art will now be briefly described in connection with the dashpots for gasoline engines. When engine acceleration is required of an automobile or the like, the throttle valve is opened. The subsequent closing of the valve, if done suddenly, would accompany the following two phenomena:
(1) Because gasoline has a larger density and develops greater inertia than each of air, the supply rate of air to the engine will decrease rapidly whereas that of gasoline will not.
(2) The sudden throttle closing will cause a sharp pressure drop in the air-fuel mixture passage on the downstream side of the throttle valve, which in turn will vaporize the gasoline that has wetted the manifold wall between the valve and the engine cylinders while the valve was open.
These phenomena will combinedly cause a prompt increase of the air-fuel mixture ratio or a temporal oversupply of gasoline for the amount of air required for combustion. This will result in incomplete combustion in the gasoline engine and hence large emissions of unburned gasoline, thermal decomposition products, carbon monoxide and other noxious substances. Should they be left out of control, the harmful emissions might well exceed the local regulation limits for anti-air pollution.
In an attempt at overcoming these difficulties, it has been customary to install a pneumatic dashpot on the closing side of the throttle valve so as to effect gradual and slow closing of the valve. Such a dashpot has a calibrated bleed orifice defined by a combination of a detachable needle and a ring-shaped opening, the cross sectional area of the opening being adjusted by the stroke of the needle.
The needle-type orifice has a rather small equivalent diameter, and the design limitations reduce the width of the flow passage to the range from 10 to 60.mu., so that the orifice can be clogged by fine dust in the air soon after use. If the orifice is clogged during operation, the dashpot will no longer work or the damping rate at the closing of the throttle valve will become much lower than expected. This will seriously affect the drivability of the vehicle at the time of deceleration or will extremely impair the engine brake effect upon releasing of the accelerator. In such an event the dashpot will have to be totally discarded and replaced by a new unit.
In order to eliminate this disadvantage, we tried to provide a fixed hole of predetermined dimensions for use as the bleed orifice of the dashpot. It was found that such a hole ranging in diameter from 0.1 to 0.3 mm gives a good result.
Like the needle-type, the fixed orifice is guarded by filters in front and in rear against the intrusion of dirt from the outside, and naturally the orifice is located rather deep in the dashpot assembly.
The afore-mentioned size and location of the fixed orifice involve the following drawbacks in the use of the dashpot having such an orifice:
(1) Since the orifice has a relatively small bore and is stationary in the dashpot, it is in the case of clogging not so easily cleaned as the needle type is. If the orifice is clogged, the entire dashpot will have to be replaced to an economic disadvantage. (with the needle type, cleaning is easier because the needle can be removed, leaving a relatively large bore behind.)
(2) The fixed orifice has a little too small bore and is located too deep in the dashpot to be machined or electrically processed conveniently for mass production.